In general, a compressor is a mechanical apparatus which receives power from a power generation apparatus, such as a motor, a turbine, or the like, and which compresses the air, refrigerant or various operating gases to raise pressure. The compressor has been widely used for electric home appliances such as refrigerators and air conditioners, and the application thereof has been expanded to the whole industry.
The compressors are roughly classified into a reciprocating compressor in which a compression space into/from which an operating gas is sucked and discharged is defined between a piston and a cylinder and the piston is linearly reciprocated in the cylinder to compress refrigerant, a rotary compressor in which a compression space into/from which an operating gas is sucked and discharged is defined between an eccentrically-rotated roller and a cylinder and the roller is eccentrically rotated along the inside wall of the cylinder to compress refrigerant, and a scroll compressor in which a compression space into/from which an operating gas is sucked and discharged is defined between an orbiting scroll and a fixed scroll and the orbiting scroll is rotated along the fixed scroll to compress refrigerant.
Particularly, the rotary compressor has been developed into a twin rotary compressor including two rollers and two cylinders at its upper and lower portions, wherein the upper and lower roller and cylinder pairs compress some and the rest of the total compression capacity, and a 2-stage rotary compressor including two rollers and two cylinders at its upper and lower portions, wherein the two cylinders communicate with each other, one pair compresses relatively low pressure refrigerant, and the other pair compresses relatively high pressure refrigerant which has been subjected to the low pressure compression.
Korean Registered Patent Publication No. 10-1994-0001355 discloses a rotary compressor. A motor is located in a shell and a rotating shaft is installed to pass through the motor. In addition, a cylinder is located below the motor, and an eccentric portion fitted around the rotating shaft and a roller fitted into the eccentric portion are located in the cylinder. A refrigerant outlet and a refrigerant inlet are formed in the cylinder, and a vane is installed between the refrigerant outlet and the refrigerant inlet so as to prevent non-compressed low pressure refrigerant from being mixed with compressed high pressure refrigerant. Moreover, a spring is installed at one end of the vane so that the eccentrically-rotated roller and the vane can be kept in contact with each other. When the rotating shaft is rotated by the motor, the eccentric portion and the roller are rotated along the inner circumference of the cylinder, compressing a refrigerant gas. The compressed refrigerant gas is discharged through the refrigerant outlet. Korean Laid-Open Patent Publication No. 10-2005-0062995 discloses a twin rotary compressor. Referring to FIG. 1, the twin rotary compressor includes two cylinders 1035 and 1045 compressing the same capacity and a middle plate 1030, and thus doubles a compression capacity as compared with a 1-stage compressor.
Korean Laid-Open Patent Publication No. 10-2007-0009958 discloses a 2-stage rotary compressor. Referring to FIG. 2, a compressor 2001 includes a motor 2014 located in an inside upper portion of a hermetic container 2013 and having a stator 2007 and a rotor 2008, and a rotating shaft 2002 connected to the motor 2014 includes two eccentric portions. A main bearing 2009, a high pressure compression element 2020b, a middle plate 2015, a low pressure compression element 2020a, and a sub bearing 2019 are successively stacked from the motor unit 2014 side with respect to the rotating shaft 2002. Additionally, a middle pipe 2040 is provided, which introduces the refrigerant compressed in the low pressure compression element 2020a into the high pressure compression element 2020b. 